Current assessment of immunotoxicity for hazard identification and mode of action utilizes a tiered approach that may include the generation of observational data, measurement of immune function and evaluation of host susceptibility to neoplastic or infectious disease. These studies are time and resource intensive. In vitro approaches for some aspects of immunotoxicity, in particular the identification of contact allergens, have been quite successful. However, while in vitro tiered testing approaches have been proposed to evaluate immunotoxicity, we currently have no reliable way reliable way to increase throughput to screen chemicals for suppression. Zebrafish offer an attractive in vitro whole animal screening and prioritization alternative to traditional rodent models because the development and function of the immune system is similar. Tracking the effects of chemicals on immune system development can be done over a shorter time span and function of the innate immune system can be assessed within days of fertilization. A consistent recommendation from workshops held with regard to the use of alternative testing methods is to generate comparative data for conventional toxicology tests and in vitro studies to support the utility of the latter for screening and prioritization. A working group of scientists from the NTP, EPA and Intergrated Laboratory Systems have designed the proposed studies to examine immunotoxicity in a zebrafish model using a panel of chemicals previously found to target the immune system using tiered testing panels in traditional rodent models.